1. Field of the Invention
The present invention relates to a data transmission apparatus, system and method and an image processing apparatus, and more particularly, to a data transmission apparatus, system and method and an image processing apparatus used in a case where an image providing device such as a digital camera is directly connected to an image processing device such as a printer via a serial interface based on, e.g., the IEEE 1394 standards.
Further, the present invention relates to a data transmission apparatus, system and method and an image processing apparatus which interconnect a plurality of electronic devices by using a data communication bus capable of performing data communication by intermixing control signals and data and among the devices.
2. Description of Related Art
Various types of systems which transfer data to a printer via a bus are known. For example, a known technique is to output data from a computer to the printer by using a defacto standard interface such as a SCSI (Small Computer System Interface) or Centronics interface.
In other words, the printer is connected to a personal computer (PC) as a host device via a parallel or serial interface such as a centronics or RS232C interface.
Further, digital devices as image providing devices such as a scanner, a digital still camera and a digital video camera, are also connected to the PC.
Image data inputted by the respective digital devices is temporarily stored in a hard disk or the like on the PC, then processed by an application software program or the like on the PC and converted into print data for the printer, and transferred via the above interface to the printer.
In the above system, the PC has driver software programs respectively for controlling the digital devices and the printer. The image data outputted from the digital devices is held by these driver software programs in data format which can be easily handled and displayed on the PC.
The stored data is converted into the print data by an image processing method in consideration of image characteristics of the input and output devices.
In this manner, the digital devices are connected to the PC as the host device, and the printer print-outputs image data provided from one of the digital devices as an image providing device, via the PC.
However, the above interface such as an SCSI interface has various inconveniences such as the low data transfer rate, the bulky communication cable, the limitation on the type and number of connectable peripheral devices, the limitation on connection methods and the like.
Further, a general PC has a large connector for connecting the SCSI interface and other cables on its rear surface. At such connector, attachment/detachment is troublesome. For example, when a portable device such as a digital still camera or a video camera is connected to the PC, it is very tiresome to connect cables to the connector provided on the rear surface of the PC.
Generally, a personal computer is already connected to a number of peripheral devices. The number of types of peripheral devices will increase, and further, by improvement of interfaces and the like, communication will be performed with a number of digital devices interconnected on a network, as well as between the personal computer with the peripheral devices. In this case, the network communication is very useful, however, as communication handling a large amount of data is frequently performed, the traffic on the network may increase and influence data communication on the network. For example, a user wants to continue image printing or to perform printing quickly while not noticing the communication traffic performed between other devices is very large. In this case, as the load on the overall network or the PC as a host device increases, the printing may not be normally performed or delayed. In this manner, the trouble occurs in data communication on the network due to increase of the network traffic or in accordance with the operational status of the PC.
On the other hand, in a new interface such as an interface based on the IEEE 1394 standards (hereinafter referred to as “1394 serial bus”), it is possible to directly connect an image providing device and a printer, thus avoiding the normal traffic.
In case of directly connecting the image providing device to the printer by the 1394 serial bus, an FCP (Function Control Protocol) operand may include print data.
Further, in the 1394 serial bus, a register area for may be provided such that data transfer is performed by writing data into the register area.
Further, as the 1394 serial bus has a plurality of data-transfer control procedures, data transfer can be performed in methods appropriate to the respective devices.
Further, to designate data transfer, a command instructing to start of data transfer and a response to the command may be employed.
As described above, the image data outputted from the image providing device is converted into print data by the PC and print-outputted by the printer, accordingly, even if the image providing device and the printer are directly connected, printing cannot be performed without the PC.
A video printer which directly print-outputs image data outputted from a digital video camera is known, however, even in case of using this printer, connection is made only between specific devices. There is no video printer which is directly connected to a number of image providing devices for general printing purposes.
That is, it is impossible to directly send image data from the image providing device to the printer for printing, by utilizing a function to directly connect devices, which is characteristic of the 1394 serial bus or the like.
In the above method which directly connects the image providing device to the printer with the 1394 serial bus and includes print data into an FCP operand, the control commands cannot be separated from the print data. Further, in this method, the transfer efficiency is low since a response is always required with respect to a command.
The above method providing a register area for data transfer requires processing to determine whether or not data can be written into the register area at every data transfer.
Accordingly, the overhead of the determination processing is great, which degrades the transfer efficiency.
Further, in the case where data transfer is designated by using a command instructing to start of data transfer and a response to the command may be employed, transmission and reception of command and response occur at each data transfer of a predetermined unit, which also degrades the transfer efficiency.